Most of the present day commercial non-ionic surfactants are prepared from petroleum or petroleum by-products. There exists an urgent need for non-ionic surfactants derived from natural sources such as carbohydrates since they offer numerous advantages. Thus, products derived from natural sources would offer a cost/performance advantage since present and future surfactant demands are dependent on formulation costs. In addition, carbohydrate-based surfactants would favorably impact critical environmental concerns such as nontoxicity and biodegradability. Moreover, carbohydrate surfactants offer raw material availability, relatively low costs and rejuvenitive capacity. All of these advantages would permit the efficient and inexpensive preparation of surfactants on a large-scale production basis.
The monomeric glucosides, e.g., methyl glucoside represent an attractive class of candidates for conversion to surfactants. Until the present time, the attachment of hydrophobic groups onto the methyl glucoside backbone required: (1) hydroxyl protection/deprotection steps, and/or (2) sequential transetherification, and/or (3) harsh or drastic reaction conditions using expensive metal hydrides. In all of these cases, the incompatibility of the materials resulting in the formation of a two-phase system made hydrophobic attachment difficult.
Methyl glucoside is prepared directly from hydrolyzed corn starch or glucose that has been treated with an acidic methanol solution according to the following equation: ##STR2##
Generally, the .alpha./.beta. anomers are formed in the ratio of 2:1. Methyl glucoside is a non-reducing sugar which exists in the pyranoside or cylic form. Reducing sugars have unstable ring structures which are easily degraded under typical glucoside derivatization conditions. The methyl glucoside structure possesses four (4) potentially reactive hydroxyl sites at which various derivatives may be formed. The relative rectivities of these hydroxyl groups differ considerably as well as their contribution to the molecule's overall polarity. Typically, the primary hydroxyl center, located at carbon position No. 6, is favored followed by the secondary hydroxyl next to the methyl aglycon, carbon position No. 2.
The conventional method for attaching acid-stable, ether-linked hydrophobes onto a glucoside-based material is performed with a hydrophobic (C.sub.12 or less) oxirane under basic conditions. Other methods include (1) addition of polymeric chains of lower oxyalkylene units (U.S. Pat. Nos. 2,407,002; 3,640,998; 4,264,478), (2) etherification of ethoxylated or propoxylated glucose (U.S. Pat. No. 3,737,426), (3) etherification of lipophilic glycosides (U.S. Pat. No. 4,011,389). In all cases, the reaction products are complex mixtures and contain acid labile hemiacetal or acetal linkages.
Acid sensitive linkages are also generated in other less commercially favorable glucoside hydrophobic attachment methods. These reactions are classified according to the following types: (1) alcoholysis with metal salts (Noller et al, J. Am. Chem. Soc., Vol. 60, p. 2076, 1938), (2) alcoholysis with acid catalysts (Wing et al, Carbohy. Res., Vol. 10, p. 441, 1969), and (3) transetherification (British Pat. No. 421,318). All of these reactions are multi-step, low yield, laborious processes which do not give well-defined products; thus, they have little practical commercial value. Regiochemical hydrophobic placement onto the glucoside molecule results in marked surface-active properties. Specifically, surfactant performance is improved by substitution on either the 3-O or 6-O position. The 6-O position is desirably etherified due to its easier accessibility.
It is an object of the present invention to provide novel and valuable non-ionic carbohydrate-based surfactants and a novel one-step, low temperature, high yield method for attaching hydrophobic groups to monomeric glucosides to form the non-ionic surfactants.